The present invention relates to a calorimeter including a combustion vessel and an integrated isothermal fluid reservoir.
In the past, somewhat complicated apparatus has been employed for the determination of the calorific value of solid and liquid substances in accordance with standard methodology (ASTM/ISO standards). The operation of such an apparatus is well understood and has been described in, for example, the American National Standard Institute ANSI/ASTM D5865.
Prior calorimeters have required the use of multiple internal and external reservoirs with which to contain and manage the water required to operate the apparatus. U.S Pat. Nos. 4,398,836 and 4,616,938 disclose calorimeters which have a tank for holding a calorimeter combustion vessel and a separate water tank coupled by conduits and valves for supplying water to the vessel. In another calorimeter disclosed in U.S. Pat. No. 4,616,938, two distinct reservoirs were employed, including an internal jacket reservoir and a permanent internal bucket reservoir. In another calorimeter disclosed in U.S. Pat. No. 5,322,360, four distinct water reservoirs are employed:                1) A first internal reservoir, commonly referred to as a jacket, is employed to provide a constant isothermal environment.        2) A second internal reservoir is employed to provide a ballast volume of water from which to fill an external burette.        3) A third external reservoir, commonly referred to as a burette, is employed to deliver a reproducible amount of analysis water.        4) A fourth transportable reservoir, commonly referred to as a bucket, is used to receive the water delivered from the burette and to contain the combustion vessel. The bucket is installed in the analyzer and temperature measurements of the bucket are recorded during the course of the analysis.        
One disadvantage of using separate reservoirs in a calorimeter is that, during routine operation, the systems require an external source of coolant water to eliminate thermal energy generated by the combustion of the sample. Also, the use of multiple reservoirs in such prior art systems requires numerous valves and conduits with which to direct the water to and from the reservoirs.
The operation of prior art isothermal calorimeters is further complicated by the requirement to maintain the temperature of the water substantially constant in all reservoirs from one analysis to the next. Additionally, upon the completion of an analysis, any heat resultant from the combustion of the sample must be removed.
Furthermore, prior art designs required the use of a distinctly separate bucket reservoir in order to ensure that the volume of water contained therein be maintained substantially constant from one analysis to the next. This requirement is a result of the fact that any variation in this volume is proportionally related to imprecision in the observed results. Assuming no other source of error, a variation of 1 part in 1000 in the volume of water will limit the precision of the apparatus, correspondingly, to 1 part in 1000.
Various instrument design approaches have been used to reduce this source of error. Typically, these approaches employ either a sensor or an overflow port with which to limit the volume of the water. Among other factors, such approaches are dependant either upon the surface tension of the water or the sensitivity and reproducibility of the sensor. In order to eliminate heat resultant from the combustion of the sample, these approaches require that the water in the bucket be substantially drained and refilled before each analysis. In some cases, the bucket and the combustion vessel must be dried by the operator in order to ensure that the correct volume of water is present.